Reversibly deformable and mechanically tunable fluidic antennas

ABSTRACT

A method of manufacturing a fluidic structure is disclosed. A cavity that defines a shape of an element of the fluidic structure within a material is formed. The cavity is filled with liquid metal. The cavity is sealed. The fluidic structure behaves as an antenna. A fluidic antenna includes a material that defines a shape of the fluidic antenna by a cavity filled with liquid metal formed within the material, where the material further defines at least one mechanical property of the fluidic antenna.

PRIORITY CLAIM

This application is a divisional of U.S. patent application Ser. No.12/889,257, filed Sep. 23, 2010; the disclosure of which is incorporatedherein by reference in its entirety.

BACKGROUND

The present invention relates to antennas. More particularly, thepresent invention relates to reversibly deformable and mechanicallytunable fluidic antennas.

Antennas provide electromagnetic signaling transmission and receptioncapabilities for electronic devices via emission and reception ofelectromagnetic radiation, respectively. For transmission, antennasconventionally convert electrical current that carries information intoelectromagnetic signals that are propagated to other devices. Forreception, antennas conventionally convert electromagnetic signalsincident upon the antenna into an electrical current that carriesreceived information.

BRIEF SUMMARY

A method of manufacturing a fluidic structure includes forming a cavitythat defines a shape of an element of the fluidic structure within amaterial; filling the cavity with liquid metal; and sealing the cavity,where the fluidic structure behaves as an antenna.

A fluidic antenna includes a material that defines a shape of thefluidic antenna via a cavity formed within the material, where thematerial further defines at least one mechanical property of the fluidicantenna; and liquid metal that fills the cavity.

A method includes receiving, via a receiving antenna of a computingdevice, a radio frequency signal transmitted via a fluidic antennacoupled to a structural element, where at least one liquid metal antennaelement is formed within a material that defines an elastomericmechanical property of the fluidic antenna and where spectraltransmission characteristics of the fluidic antenna change in responseto changes in shape of the fluidic antenna; determining a resonantfrequency of the radio frequency signal; and determining a strain on thestructural element based upon the determined resonant frequency of theradio frequency signal.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an illustration of an example of an implementation of areversibly deformable and mechanically tunable single element (e.g.,single pole) fluidic antenna according to an embodiment of the presentsubject matter;

FIG. 2 is a detailed illustration of an example of an implementation ofa base material that defines a shape of the fluidic antenna of FIG. 1according to an embodiment of the present subject matter;

FIG. 3 is a detailed illustration of an example of an implementation ofthe base material sealed to the bonding layer material of the fluidicantenna of FIG. 1 according to an embodiment of the present subjectmatter;

FIG. 4 is a detailed illustration of an example of an implementation ofa process of injecting liquid metal into the cavity formed within thebase material as sealed by the bonding layer material to form thefluidic antenna of FIG. 1 according to an embodiment of the presentsubject matter;

FIG. 5 is an illustration of an example of an implementation of areversibly deformable and mechanically tunable dipole (dual element)fluidic antenna according to an embodiment of the present subjectmatter;

FIG. 6 is an illustration of an example of an implementation of a set ofresonant frequency response curves for a fluidic dipole antenna, such asthe fluidic antenna, under different strain conditions (e.g., tensionand compression forces) according to an embodiment of the presentsubject matter;

FIG. 7 is a block diagram of an example of an implementation of a strainsensing system that utilizes the reversibly deformable and mechanicallytunable dipole fluidic antenna of FIG. 5 according to an embodiment ofthe present subject matter;

FIG. 8 is a flow chart of an example of an implementation of a processfor manufacturing a reversibly deformable and mechanically tunablefluidic antenna as a fluidic structure according to an embodiment of thepresent subject matter;

FIG. 9 is a flow chart of an example of an implementation of a processfor manufacturing a reversibly deformable and mechanically tunablefluidic antenna using a two-part substrate according to an embodiment ofthe present subject matter;

FIG. 10 is a flow chart of an example of an implementation of a processfor determining a strain on one or more structural elements using areversibly deformable and mechanically tunable fluidic antenna accordingto an embodiment of the present subject matter; and

FIG. 11 is a flow chart of an example of an implementation of a processdetermining a strain on one or more structural elements using a set ofreversibly deformable and mechanically tunable fluidic antennas andlogging device identifiers associated with determined strain readingaccording to an embodiment of the present subject matter.

DETAILED DESCRIPTION

The examples set forth below represent the necessary information toenable those skilled in the art to practice the invention and illustratethe best mode of practicing the invention. Upon reading the followingdescription in light of the accompanying drawing figures, those skilledin the art will understand the concepts of the invention and willrecognize applications of these concepts not particularly addressedherein. It should be understood that these concepts and applicationsfall within the scope of the disclosure and the accompanying claims.

The subject matter described herein provides reversibly deformable andmechanically tunable fluidic antennas. The reversibly deformable andmechanically tunable fluidic antennas may be formed by injecting aliquid metal, such as gallium or a gallium-based alloy, into one or morecavities within a material substrate or a base material coupled to abonding layer material. However, it is understood that any liquid metalthat has a melting point below an ambient liquid metal antennamanufacturing facility temperature may be used such that heating of theliquid metal is not required. It is understood that any givenmanufacturing facility may be operated at a different temperature asappropriate for a given implementation. An example temperature rangefrom negative twenty degrees Celsius (−20° C.) to forty degrees Celsius(40° C.) may be used in association with certain of the metals describedherein that are in a liquid state within this range, though it isunderstood that other temperature ranges may be appropriate for anygiven liquid metal to be used to form a reversibly deformable andmechanically tunable fluidic antenna. For example, eutectic galliumindium (EGaIn) has a melting point of fifteen and seven tenths degreesCelsius (15.7° C.). As such, a lower end of the ambient liquid metalantenna manufacturing facility temperature range for such animplementation may be considered, for example, sixteen degrees Celsius(16° C.). Other metals and temperature ranges may be used for formationof liquid metal antennas that may have higher or lower melting points,and as such, different ambient liquid metal antenna manufacturingfacility temperature ranges.

As an alternative to injecting a liquid metal into one or more cavities,the liquid metal may be drawn into a cavity by applying a vacuum orother pulling force to the liquid metal via the cavity. In eitherimplementation, injecting or drawing the liquid metal into the cavitymay be terminated in response to the cavity filling to capacity.Alternatively, filling the cavity may be terminated on demand bycessation of the filling process upon filling of the cavity to an extentsufficient to allow radiation of electromagnetic energy via the fluidicantenna. Inlet and outlet filling hole locations may be provided for therespective operations, and the cavity may be sealed in response tofilling the cavity.

The term “fluidic antenna” and “liquid metal antenna” may be usedinterchangeably to represent an antenna with a liquid metal resonantelement. The term “material” and “substrate” may be used interchangeablyto represent a substance within which a fluidic antenna may be formed.The term “cavity” may be used to represent a hollow channel, capillary,conduit, groove, furrow or other structure within a substrate withinwhich liquid metal may be filled to form a fluidic antenna. The terms“cavity,” “channel,” and “capillary” or other terms may be usedinterchangeably hereafter to identify a void or other structure, withinone or more portions of material that define a shape of a fluidicantenna within the material, that may be filled with liquid metal toform a fluidic antenna. For certain implementations, a channel may beconsidered a “microfluidic channel.”

The material within which the cavity and fluidic antenna are formed mayinclude a flexible material, for example, an elastomer such as siliconeor other polymer-based materials. Other examples of flexible materialsinclude polymer films, composite substrates, gels, thin metal supports,and other flexible materials. The material within which the cavity andfluidic antenna are formed may also include rigid materials such aswood, dry wall, polymeric parts, polymer films, gels, and other rigidmaterials. It is understood that the present subject matter applies toany material that may form a cavity that may define a shape of a fluidicantenna without interfering with spectral properties of the fluidicantenna beyond interference acceptable within a given implementation,and all such materials are within the scope of the present subjectmatter.

A cavity may be formed into a substrate in a variety of manners. Becausethe antenna is formed with a liquid metal, the mechanical properties ofthe antenna may be defined by mechanical properties of the substrate. Assuch, for an elastomeric substrate, the resulting elastomeric fluidicantenna may be deformed (e.g., stretched, bent, flexed, rolled, etc.)and released/reversed without loss of electrical continuity. As aconsequence, the resulting antennas may be more durable relative toconventional technologies and may be utilized in applications that wouldotherwise result in destruction of conventional antennas. Strain may beinduced in a material, for example, in response to temperature changes,pressure changes, mechanical load changes, geographical changes, or anyother change that results in a force on the material that deforms,elongates, shrinks, or otherwise changes the material's dimensions. Forexample, the fluid metal may flow in response to strain (e.g.,elongation) of the elastomeric substrate, resulting in a reconfigurationof the geometry of the fluidic antenna and a resulting shift in theresonant frequency of the antenna, while returning to its originalgeometry and frequency response upon removal of the applied strain.Based upon these properties, the fluidic antenna is considered to haveno or minimal hysteresis, as defined by the mechanical properties of thesubstrate in response to mechanical strain and release of mechanicalstrain.

As one example of channel formation within a two-part substrate,lithography, such as soft lithography or photolithography, may be usedto form one or more channels within an elastomer that represents oneportion of the two-part substrate. A “master” pattern of a negativeshape of the channel may be generated on a silicon wafer using anegative photoresist (e.g., an epoxy-based SU-8 photoresist, Microchem,etc.). The pattern may be dimensioned according to a configured resting(e.g., non-elongated) dimension and resonant frequency of the fluidicantenna. An elastomer pre-polymer may be cured against thetopographically patterned substrate described above, for example byreplica molding, to produce an inverse replica of the master pattern ofa negative shape of the channel with the portion of the two-partsubstrate. The elastomer may be exposed to a substance or stimulus, suchas oxygen plasma, to help adhere the interface to another sheet ofelastomer. The first portion of the two-part substrate may then befurther processed by sealing a bonding layer material to the substrateand filling the channel with liquid metal, as described in more detailbelow.

Fluidic antenna models may be constructed and simulated numericallyunder multiple operating conditions using computational electromagneticmethods, such as, for example, finite element method (FEM) modeling orother computational electromagnetic method as appropriate for a givenimplementation. The replica molding described above may be utilized forrapid prototyping of new antenna designs, where a single “master” may bereplicated to produce many identical antennas. As such, the presentsubject matter may further reduce new antenna design time.

The elastomer or elastomer pre-polymer as described above may include,for example, polydimethylsiloxane (PDMS). PDMS is a silicone elastomer,and has a low dielectric constant (on the order of 2.67) and adielectric loss tangent (ranging from, for example, 0.001 at 100 kHz to0.04 at 77 GHz). PDMS is highly elastic with a low Young's modulus(e.g., tensile modulus) of less than two megapascals (<2 MPa) and a lowsurface energy, thereby providing one example of a substrate that mayprovide adequate stretchability, deformability, and recoverabilitysuitable for use in association with the present subject matter. PDMSmay further conform to surfaces based upon these properties. As such,antennas of a variety of forms and shapes may be constructed based uponchannel dimensions and form, in conjunction with mounting forms for thefinished fluidic antenna.

As one example of an antenna that may be implemented utilizing thepresented subject matter, a dipole antenna does not have significantresonant fields within a surrounding dielectric. As such, fielddensities inside a substrate such as PDMS are relatively low.Accordingly, PDMS represents one suitable casing/substrate material fordipole antennas. It is understood that many other possibilities existfor an elastomeric substrate and that certain materials may be suited tocertain antenna geometries, and all such possibilities are consideredwithin the scope of the present subject matter.

Example antenna designs that may benefit from the present subject mattermay include fluidic antennas formed as a single element (e.g., singlepole) antenna, a dipole antenna, a helix antenna, a coil antenna, apatch antenna, a swiss-cross antenna, a bow-tie antenna, a microstripantenna, a horn antenna, a planar-inverted F-shaped antenna (PIFA), andan array of antennas. Many other variations on antenna design arepossible using the present subject matter and all are considered withinthe scope of the present subject matter.

A fluid metal that includes a low-viscosity liquid at a manufacturingfacility temperature may be used to form the fluidic antenna(s). Lowtemperature liquid metals (e.g., metals or metal alloys that remainfluidic at room temperature) may include alloys that are gallium (Ga)based. One example of a fluid metal that may be suitable for use inassociation with the present subject matter is eutectic gallium indium(EGaIn). EGaIn is a low viscosity (e.g., approximately twice theviscosity of water) liquid metal alloy at room temperature with arelatively high conductivity (on the order of σ=3.4×10⁴ Scm⁻¹ (siemensper centimeter)). EGaIn has a relatively low level of toxicity (e.g.,compared to mercury or certain other substances) and may form conductiveand mechanically stable structures in cavities, such as microfluidicchannels or capillaries. EGaIn does not need to be heated prior toinjection because it is a liquid at room temperature. Further, EGaInmaintains its fluidity after injection. As such, EGaIn may maintaincontinuity during deformation at many operating temperature conditions.

It is understood that liquids have surface tension that causes them toadopt a shape that minimizes the surface energy without external forcesapplied, such as for example a spherical shape. However, EGaIn forms apassivating oxide layer (e.g., it does not grow thicker with time) thatprovides mechanical stability to the liquid metal such that it maymaintain its non-spherical structure in the microfluidic channelsdespite its high surface tension. As such, any material, such as EGaIn,that creates a thin oxide skin once filled into the microfluidicchannel(s) and that provides mechanical stability to the fluid withinthe microfluidic channels may be suitable for use in association withthe present subject matter. It is understood that many otherpossibilities exist for liquid metal antenna construction and all areconsidered within the scope of the present subject matter.

As described above, the metal described herein as an example for usewith fluidic antennas is EGaIn. It should be understood that EGaIn isused herein for the purposes of example and that any conductive liquids,such as liquids with suspended metallic nanoparticles, that possessessimilar properties may be used. EGaIn has a composition of approximately75% Gallium (Ga) and 25% Indium (In) by weight, and has a melting point(m.p.) of fifteen and seven tenths degrees Celsius (15.7° C.). Atambient manufacturing facility temperatures, the EGaIn may fill thechannel(s) rapidly. The EGaIn has a relatively high surface energy.However, once injected, the EGaIn creates a thin metal-oxide “skin” thatkeeps the fluid mechanically stable inside of the microfluidic channelsdespite the high surface energy of the metal. Further, an operatingrange for purposes of deformation and reconfiguration of a fluidicantenna constructed using EGaIn may be, for example, any temperatureabove 15.7° C. as based further upon properties of the substratematerial. Other alloys, such as those that contain tin (Sn) or otheralloys, may have a lower temperature range (e.g., melting point) for aliquid state. However, it should be noted that a fluidic antenna may beused below the melting point temperature of the liquid metal, thoughwith possibly reduced reflow rates based upon the liquid metal used inany given implementation.

EGaIn is a low viscosity fluid. However, it should be noted that otherfluids exist that may be utilized to form a reversibly deformable andmechanically tunable fluidic antenna, and all are considered within thescope of the present subject matter. As such, the elastomeric cavitiesdefine the mechanical properties of the antenna. The fluidic antennasresist permanent deformation (e.g., the antennas may return to theiroriginal state after removal of an applied stress). As such, theantennas may be deformed (e.g., stretched, bent, rolled, and twisted)reversibly without permanent mechanical or electrical hysteresis losses.

Because the conductive element of the fluidic antenna is a fluid (e.g.,liquid metal), the mechanical properties and shape of the antenna aredefined by the elastomeric substrate. The antennas may withstand appliedstrain that results in mechanical deformation (e.g., stretching,bending, rolling, and twisting, etc.) and return to their original stateafter removal of an applied strain due to the elastomeric properties ofthe substrate. The ability of the liquid metal to flow duringdeformation of the antenna provides electrical continuity during theapplied strain. Accordingly, the shape, and as a result the function, ofthe antenna is reconfigurable.

The resonant frequency of the fluidic antenna(s) may be tunedmechanically by deforming the fluidic antenna via stretching, bending,twisting or other mechanical strain without hysteresis during strainrelaxation. The ability to reconfigure the shape of the fluidic antennaand to tune the spectral response of fluidic antennas mechanically makesthem suitable for sensing external forces. As such, the fluidic antennasmay be used as sensors of strain in addition to being used inenvironments where impacts and other mechanical actions may be impartedonto antennas.

A fluidic antenna may further be elongated during mounting to bias theantenna to a known biased resonant frequency. Deviations in that biasedresonant frequency as a result of compression or expansion of thefluidic antenna may then be detected. As such, the fluidic antenna maybe used to sense contraction and expansion of building, bridge, vehicle,or other mechanical fastening locations or construction joints.

The liquid metal may also facilitate self-healing (e.g., they regaintheir conductivity) after removal of a razor blade or other sharpobjects that create sharp cuts (e.g., across an axis of a fluidicantenna element) as long sufficient substrate material is present toallow the liquid metal to reflow and to allow the liquid metal on eachside of the cut location to make contact and re-bond. It should be notedthat under such circumstances, based upon the dimensionality of a givenimplementation, such a cut may create two distinct metal-air interfacesand the liquid metal may remain flush with the cut interface (i.e., notreflow into or out of the channel). The oxide skin may get “pinned” tothe edges of the opening in the channel created by the cut location.When the antenna is relaxed after the sharp object is removed, it mayreturn to its original conducting state provided sufficient mechanicalintegrity remains to allow the base material elastomer to contract backto its original shape. Pressing on the channels may cause the two metalinterfaces to merge into a continuous element. As such, the softinterface of the fluidic antenna may facilitate reliable healing undermoderate mechanical impacts.

Flexible fluidic antennas may be used in association with other flexibleelectronics by incorporation of electronics and sensors into flexiblesubstrates such as textiles (e.g., fabrics), displays, and bandageswithout loss of ergonomic functionality of the respective textile.Flexible electronics may further utilize fluidic antennas to providesensing or wireless communication capabilities. Many possibilities existfor flexible electronic applications based upon the subject matterdescribed herein and all are considered within the scope of the presentsubject matter.

For example, detection of motion may be possible with fluidic antennascoupled to textiles and bandages to determine mobility or other factors.Physical rehabilitation and athletic analysis may also utilize fluidicantennas for determination of athletic performance and progress afterinjury. Many other possibilities exist for use of fluidic antennas infabrics and all are considered within the scope of the present subjectmatter.

The ability to reversibly deform the fluidic antennas may also be usedin association with compact deployment where such materials are, forexample, rolled for shipping and unrolled for remote deployment. Use ofantennas constructed of liquid metal during shipping via compactdeployment may also increase durability and avoid damage.

The bendable nature of the fluidic antennas described herein makes themsuitable for “smart antenna” applications. Beam-forming and beam-bendingmay be achieved via the mechanical properties of fluidic antennas. Thesedevices may be useful, for example, in millimeter-wave applications(e.g., automotive radars, security and surveillance systems, andhigh-data rate wireless communication systems). Fluidic antennas mayfurther be utilized in applications in which a portion of the antenna isintended to bend out of plane, such as mechanically scanned antennas, toimprove on applications that utilize conventional electronics, such aselectronic phase shifting arrays.

The fluidic antennas described herein may also provide improvement overconventional antennas, such as copper or other solid metal antennas,that are limited in the extent to which they can be stretched. Further,because the fluidic antennas may be encapsulated within an elastomericsubstrate, fluidic antennas may further improve durability, and as such,reliability, of applications that have previously used conventionalsolid metal antennas.

The reversibly deformable and mechanically tunable fluidic antennasdescribed herein may be manipulated in real time to allow promptfrequency shifting of the resonant frequency of the antennas. Forpurposes of the present description, real time shall include any timeframe of sufficiently short duration as to provide reasonable responsetime for information processing acceptable to a user of the subjectmatter described. Additionally, the term “real time” shall include whatis commonly termed “near real time”—generally meaning any time frame ofsufficiently short duration as to provide reasonable response time foron-demand information processing acceptable to a user of the subjectmatter described (e.g., within a portion of a second or within a fewseconds). These terms, while difficult to precisely define are wellunderstood by those skilled in the art.

It is further understood that the shape, dimensions, and othergeometries associated with the fluidic antennas described below inassociation with FIG. 1 through FIG. 6 are for illustration purposesonly and are not to scale. It is understood that appropriate dimensionsmay be chosen for a given application based upon the description below.

FIG. 1 is an illustration of an example of an implementation of areversibly deformable and mechanically tunable single element (e.g.,single pole) fluidic antenna 100 (fluidic antenna 100 hereafter). It isunderstood that the reversibly deformable and mechanically tunablesingle element fluidic antenna 100 is described herein to detail certainaspects of manufacturing for reversibly deformable and mechanicallytunable fluidic antennas.

It is understood that the fluidic antenna 100 may operate, for example,as a monopole, quarter-wave antenna when extended above a ground plane.The ground plane is omitted for ease of illustration purposes. However,it is understood that any suitable ground plane may be used or may beomitted as appropriate for a given implementation. A quarter-waveantenna resonates with a wavelength, λ, that is approximately four timesthat of the total antenna length, L (λ=4 L) and is inverselyproportional to the resonant frequency (λ=cv⁻¹, where v is the resonantfrequency, and c is the speed of light). It is further understood that aresonant frequency of the fluidic antenna 100 is proportional to thephysical length, L, and may be changed by elongating the fluidic antenna100, such as in response to strain on a structural element to which thefluidic antenna 100 is mounted. As discussed above, strain may beinduced in a structural element, for example, in response to temperaturechanges, pressure changes, mechanical load changes, geographicalchanges, or any other change that results in a force on the structuralelement that deforms, elongates, shrinks, or otherwise changes thestructural element. As such, a resonant frequency change associated withthe fluidic antenna 100 may be used to determine a stress on astructural element (e.g., a tensile strain or a compressive strain) inresponse to a determination of the resonant frequency change, asdescribed in more detail below beginning with FIG. 7 for an example ofdipole antenna strain sensing implementation.

A base material 102 may be formed of any elastomeric or rigid material,such as a low dielectric constant low-loss tangent elastomer. Siliconesrepresent a category of elastomers. However, there are several otherembedding materials including several types of polymers (e.g.,polybutadiene, polyisoprene, polysulfide rubber, silicone rubber,polyacrylic, co-polymers, ethylene vinyl acetate, etc.) that may be usedas a substrate. A channel 104 is formed within the base material 102.

A bonding layer material 106 is sealed to the base material 102 toenclose/encase the channel 104 to form a cavity within the substrate.For use in association with an elastomer, a sealing process such asoxygen plasma may be used to seal the bonding layer material 106 to thebase material 102.

The channel 104 defines a shape of the fluidic element of the fluidicantenna 100, while the selection of the elastomer for the base material102 and the bonding layer material 106 defines one or more mechanicalproperties (e.g., elasticity, flexibility, etc.) for the fluidic antenna100.

As such, mechanical properties of the fluidic antenna 100 may be definedand/or modified by selection of dimensions of the material 102 inconjunction with the bonding layer material 106. For certainimplementations, such as strain sensing, the dimensions of the basematerial 102 and the bonding layer material 106 may be chosen based uponmechanical properties of a structural element upon which the fluidicantenna 100 is to be used to sense strain along with a resolution ofresonant frequency of the fluidic antenna 100 that may be sensed withinthe given implementation environment.

A filling hole 108 and a filling hole 110 are shown in a cross-hatchedmanner to represent that they are sealed. The filling hole 108 and thefilling hole 110 may be sealed, for example, by use of additionalelastomeric material. The filling hole 108 and the filling hole 110 maybe used to fill the channel 104 with liquid metal, and sealed inresponse to completion of the filling operation. The liquid metal mayinclude a liquid metal that forms an oxidized layer that stabilizes theliquid metal within the channel 104 after the channel 104 is filled.However, while the present example illustrates a low-viscosityhigh-surface tension liquid metal, it is understood that a low viscosityand high surface tension liquid metal is not required. Any liquid metalthat may be encapsulated within a cavity of a substrate may be used asappropriate for a given implementation. A liquid metal, such as eutecticgallium indium (EGaIn), may be used as the liquid metal for a fluidicantenna, such as the fluidic antenna 100. However, other liquid metalsmay be used, including several other gallium-based alloys.

Filling the channel 104 with the liquid metal may include eitherinjecting the liquid metal into the channel 104 using the filling hole108, for example, as an injection location. Injection of the liquidmetal into the channel 104 may be terminated, for example, in responseto the liquid metal flowing toward an outlet location of the channel104, such as out the filling hole 110. Alternatively, the channel 104may be filled with the liquid metal by drawing the liquid metal into oneof the filling hole 108 and the filling hole 110 via a force, such as avacuum, until the liquid metal emerges from the other of the fillinghole 108 and the filling hole 110 or is filled to the desired locationas appropriate for a given implementation.

It is understood that a rigid material with similar electricalproperties to the base material 102 and the bonding layer material 106described above may be used as appropriate for a given implementation.For example, in situ manufacturing of a fluidic antenna in associationwith a rigid circuit board or other implementation may be performedwithout requiring use of an elastomeric substrate. The ability of thefluid metal to alloy with many metals may further facilitate the directelectrical connection and incorporation of antennas onto substratesfeaturing electronic components for a variety of applications. Manypossibilities exist for implementation of the subject matter describedherein into electronic applications and all are considered within thescope of the present subject matter.

A detailed description of the various elements of the fluidic antenna100 and a process for manufacturing the fluidic antenna 100 aredescribed below beginning with FIG. 2. An additional example of a dipoleantenna is described below beginning with FIG. 5.

FIG. 2 is a detailed illustration of an example of an implementation ofthe base material 102 that defines a shape of the fluidic antenna 100 ofFIG. 1. Regarding the fabrication/manufacturing of the base material 102including the channel 104 for defining a shape of the fluidic antenna100, photolithography, for example, may be used to generate a “master”pattern of a negative shape of the channel 104 on a silicon wafer usinga negative photoresist (e.g., an epoxy-based SU-8 photoresist,Microchem, etc.). The pattern may be dimensioned according to aconfigured resting (e.g., non-elongated) dimension and resonantfrequency of the fluidic antenna 100.

To form the base material 102, an elastomer pre-polymer (e.g., PDMS) maybe cured against the topographically patterned substrate describedabove, for example by replica molding, to produce an inverse replica ofthe master pattern of a negative shape of the channel 104. The finalbase material 102 may then be further processed as described inassociation with FIG. 3 below.

With reference to FIG. 2, a channel depth 112 and a channel width 114may be configured and may be selected based upon a configured volume ofliquid metal, in conjunction with a channel length 116, to allow theliquid metal to flow under strain (e.g., elongation) and maintainconductivity. Presuming a fluidic antenna is in the low Gigahertz (GHz)range, an example dimension for the channel depth 112 may include adepth on the order of one hundred and fifty micrometers (150 μm) deepwith a range/deviation from this example dimension on the order of fiftymicrometers (50 μm) as appropriate for the given implementation. Anexample channel width 114 may include a width of one half millimeter(0.5 mm) wide with a range/deviation from this example dimension on theorder of one tenth of a millimeter (0.1 mm) as appropriate for the givenimplementation. It is understood that a person of ordinary skill wouldbe able to perform a mathematical calculation utilizing the quarter-waveequation(s) described above to arrive at an appropriate channel length116 for a given target resonant frequency based upon the descriptionherein. However, again presuming a fluidic antenna in the low GHz range,an example channel length 116 may include a length of twenty five andfour tenths millimeters (25.4 mm) long, with a range/deviation from thisexample dimension on the order of one millimeter (1 mm) as appropriatefor the given implementation. It should be noted that the presentexample provides certain dimensions, any dimensions appropriate for agiven implementation may be used without departure from the scope of thepresent subject matter. For example, thickness of the liquid metalwithin the channel may be chosen based upon matching the dimensions ofthe liquid antenna to a feed that supplies signaling to the liquidantenna. Many other possibilities exist for dimensional selection.Additionally, other dimensions are possible as appropriate for a givenimplementation and all are considered within the scope of the presentsubject matter. Chosen dimensions may be verified by a verificationprocess, such as profilometry.

As described above, dimensions (not labeled) of the base material 102may be chosen as appropriate for a given implementation in conjunctionwith the dimensions of a bounding material, such as the bonding layermaterial 106, to arrive at final resting (e.g., non-elongated)dimensions for the fluidic antenna. For example, where a high resistiveforce is desired to counter strong strain forces, the dimensions of thebase material 102 in conjunction with the bonding layer material 106 maybe greater than an implementation where a relatively lower resistiveforce is desired to counter a lower relatively strain force.

FIG. 3 is a detailed illustration of an example of an implementation ofthe base material 102 sealed to the bonding layer material 106 of thefluidic antenna 100 of FIG. 1. As can be seen from FIG. 3, the bondinglayer material 106 is represented as a flat material (e.g., PDMS ofabout ˜1 mm thickness for a low GHz resonant frequency fluidic antenna).The bonding layer material 106 may be sealed to the base material 102 toproduce a microfluidic channel or capillary into which the liquid metalmay be injected or into which the liquid metal may be drawn. The bondinglayer material 106 may be sealed to the base material 102 by oxygenplasma modification of the interface.

A hole 118 and a hole 120, each located proximate to one end of thechannel 104 provide entry and exit paths for the liquid metal duringfilling of the channel 104, and allow for air in the channel 104 to beexpelled when the channel 104 is filled with the liquid metal.

It should be noted that one of the hole 118 and the hole 120 may beformed by a liquid metal injection device (See FIG. 4) punched throughthe bonding layer material 106. As such, only one of the hole 118 andthe hole 120 needs to be formed prior to injection. For a manufacturingprocess where liquid metal is to be drawn into the channel 104, one ofthe hole 118 and the hole 120 may be coupled to a vacuum system (notshown), while a liquid metal reservoir supply feed (also not shown) maybe fitted to the other of the hole 118 and the hole 120 to allow theliquid metal to be drawn into the channel 104 via the vacuum forcegenerated by the vacuum system. Many other possibilities exist forfilling a microfluidic channel, such as the channel 104, and all areconsidered within the scope of the present subject matter.

FIG. 4 is a detailed illustration of an example of an implementation ofa process of injecting liquid metal into the channel 104 formed withinthe base material 102 as sealed by the bonding layer material 106 toform the fluidic antenna 100 of FIG. 1. As can be seen from FIG. 4, aliquid metal injection device 400 is shown inserted into the hole 118with liquid metal flowing into the channel 104 and out of the hole 120,as represented by the arrows 402 and 404, respectively. It should benoted that an additional thin-layer of elastomer (e.g., PDMS) may beused to seal the hole 118 and hole 120 of the cavity to assist withhandling after filling the channel 104 to form the fluidic antenna 100.

FIG. 5 is an illustration of an example of an implementation of areversibly deformable and mechanically tunable dipole (dual element)fluidic antenna 500 (fluidic antenna 500 hereafter). It is understoodthat the fluidic antenna 500 may operate, for example, as a half-waveantenna. A half-wave antenna resonates with a wavelength, λ, that isapproximately two times that of the total antenna length, L (A, =2 L)and is inversely proportional to the resonant frequency (λ=cv⁻¹, where vis the resonant frequency, and c is the speed of light). It is furtherunderstood that a resonant frequency of the fluidic antenna 500 may bechanged by elongating the fluidic antenna 500, such as in response tostrain on a structural element to which the fluidic antenna 500 ismounted. As such, a resonant frequency change associated with thefluidic antenna 500 may be used to determine a stress on a structuralelement (e.g., a tensile stress or a compressive stress) in response toa determination of the resonant frequency change, as described in moredetail below beginning with FIG. 7 for an example of dipole antennastrain sensing implementation.

It is understood that a dipole antenna includes two conductive rods ofequal length that are aligned along their long axis and separated by aninsulating gap. Each fluidic element of a dipole fluidic antenna, suchas the fluidic antenna 500, may be aligned along their length axis andseparated by a gap. The gap may include, for example, any gap (e.g., 2mm) appropriate for a given implementation of a fluidic dipole antennain the low GHz range.

A base material 502 may be formed, as described above for the fluidicantenna 100, of any elastomeric or rigid material, such as a lowdielectric constant low loss tangent elastomer. Silicones represent acategory of such elastomers. However, there are several other embeddingmaterials including several types of polymers (e.g., polybutadiene,polyisoprene, polysulfide rubber, silicone rubber, polyacrylic,co-polymers, ethylene vinyl acetate, etc.) that may be used as asubstrate.

A channel 504 and a channel 506 are formed within the base material 502.The channel 504 and a channel 506 formed within the base material 502may each be formed similarly to the description above for the channel104 of the fluidic antenna 100. As such, reference to the description ofthe fluidic antenna 100 and FIG. 1 through FIG. 4 provides appropriatedetails of the channel 504 and the channel 506 formed within the basematerial 502.

It should be noted that the channel 504 and a channel 506 formed withinthe base material 502 may be separated by a distance 508. The distance508 may be selected as appropriate for a given implementation. Oneexample for a fluidic antenna in the low GHz range may include adistance on the order of millimeters (e.g., 2 mm) While the presentexample describes certain dimensions, it is understood that anydimensions appropriate for a given implementation may be used. Otherdimensions are possible as appropriate for a given implementation andall are considered within the scope of the present subject matter.

A bonding layer material 510 is sealed to the base material 502 toenclose/encase the channel 504 and a channel 506 to form two cavitieswithin the substrate. For use in association with an elastomer, asealing process such as oxygen plasma may be used to seal the bondinglayer material 510 to the base material 502.

The channel 504 and a channel 506 each define a shape of one fluidicelement of the fluidic antenna 500, while the selection of the elastomerfor the base material 502 and the bonding layer material 510 defines oneor more mechanical properties (e.g., elasticity, flexibility, etc.) forthe fluidic antenna 500.

As such, mechanical properties of the fluidic antenna 500 may be definedand/or modified by selection of dimensions of the base material 502 inconjunction with the bonding layer material 510. For implementations,such as strain sensing, the dimensions of the base material 502 and thebonding layer material 510 may be chosen based upon mechanicalproperties of a structural element upon which a fluidic antenna is to beused to sense strain, along with a resolution of resonant frequency ofthe fluidic antenna 500 that may be sensed within the givenimplementation environment.

A filling hole 512 and a filling hole 514 are associated with thechannel 504 and are shown in a cross-hatched manner to represent thatthey are sealed. A filling hole 516 and a filling hole 518 areassociated with the channel 506 and are shown in a cross-hatched mannerto represent that they are sealed.

The filling hole 512 through the filling hole 518 may be sealed, forexample, by use of additional elastomeric material. The filling hole 512and the filling hole 514 may be used to fill the channel 504 with liquidmetal, while the filling hole 516 and the filling hole 518 may be usedto fill the channel 506 with liquid metal, as described above inassociation with FIG. 4. The filling hole 512 through the filling hole518 may be sealed in response to completion of the filling operation forthe respective cavities. The liquid metal may include a low-viscosityhigh-surface tension liquid metal that forms an oxidized layer thatstabilizes the liquid metal within the channel 504 and the channel 506after the respective cavity is filled. A liquid metal, such as eutecticgallium indium (EGaIn), may be used as the liquid metal for a fluidicantenna, such as the fluidic antenna 500. Filling of the channel 504 andthe channel 506 with the liquid metal may be performed as describedabove in association with FIG. 1 through FIG. 4.

It is understood that a rigid material with similar electricalproperties to the base material 502 and the bonding layer material 510described above may be used as appropriate for a given implementation.For example, in situ manufacturing of a fluidic antenna in associationwith a rigid circuit board or other implementation may be performedwithout requiring use of an elastomeric substrate. Many possibilitiesexist for implementation of the subject matter described herein and allare considered within the scope of the present subject matter.

An arrow 520 illustrates a direction of elongation of the fluidicantenna 500. As the fluidic antenna 500 is stretched relative to an axisof the fluidic antenna 500 (not shown) proximately parallel to the arrow520, the channel 504 and the channel 506 will elongate. A distance ofstretch (e.g., length plus a delta length) of the respective channelsand the new total length of the fluidic antenna 500 may be used inconjunction with the half-wave equation described above to determine anew resonant frequency. It is understood that an increased length mayresult in a lower resonant frequency.

Similarly, the fluidic antenna 500 may be mounted with a biasedelongation (e.g., longer than its resting non-elongated length) and abiased resonant frequency may be determined Using a biased elongationand biased resonant frequency, tension and compression forces may bedetermined. Elongation (e.g., tension) and contraction (e.g.,compression) of the fluidic antenna 500 may be determined, by, forexample, a decrease and an increase in the resonant frequency relativeto the bias resonant frequency, respectively. Reference is again made tothe half-wave equation above for mathematical reference. Manypossibilities exist for strain and stress measurement based upon thepresent subject matter and all are considered within the scope of thepresent subject matter.

Regarding testing and verification associated with spectral propertiesof a fluidic antenna as described herein, or circuitry forimplementation and driving such a fluidic antenna, a series networkanalyzer or similar circuitry may be used to measure the spectralproperties of the fluidic antenna 100 or the fluidic antenna 500, or adifferent fluidic antenna. Using the fluidic antenna 500 as an example,a balanced-to-unbalanced (e.g., balun) transformer may be used to drivethe fluidic antenna 500. The balanced-to-unbalanced transformer mayconvert an “unbalanced” (e.g., grounded) coaxial cable from the networkanalyzer to a “balanced” (e.g., ungrounded) antenna input.

Given the elastomeric properties of the fluidic antenna constructiondescribed herein, solder or other types of circuit connectivity are notneeded. Leads for connection to circuitry to drive or receive signalingmay be inserted directly into the fluidic liquid metal antenna elements,such as the channel 504 and the channel 506. Insertion of the leads maybe proximate to the filling hole 514 and the filling hole 516,respectively, for the fluidic antenna 500. Continuity may be achievedvia the fluidic surface contact of the respective leads to the liquidmetal filled within the channel 504 and the channel 506. Accordingly,installation complexity of strain sensor circuitry on bridges orbuildings may be significantly reduced and safety may be improved by useof the fluidic antennas described herein.

To provide additional detail regarding verification and circuitperformance of a fluidic antenna as described herein, the networkanalyzer may transmit incident electromagnetic waves into a fluidicantenna and measure the amount of energy reflected back to the networkanalyzer as a function of frequency. The reflection coefficient, Γ,represents a ratio of the reflected voltage and the incident voltage.For each frequency in a frequency sweep, the network analyzer maycalculate a reflection coefficient. The reflection coefficient may berepresented in decibels (dB). In decibels, the reflection coefficient,or return loss, may be represented as negative twenty multiplied by alogarithm of a magnitude of a complex form of the reflection coefficient(e.g., −20 log |Γ|) where |Γ| is the magnitude of the complex reflectioncoefficient. The frequency with the lowest return loss represents theresonant frequency of the antenna. As described below in associationwith FIG. 6, the resonant frequency may be changed by elongation of afluidic antenna, such as the fluidic antenna 500.

Spectral properties and efficiency of a fluidic antenna, such as thefluidic antenna 500, may be characterized in “free space” position(e.g., not stretched or clamped). A fluidic antenna formed as describedherein may resonate, for example, a configured frequency withapproximately ninety percent (≈90%) radiation efficiency as measured bya far-field, anechoic chamber. The radiation efficiency may be definedas a ratio of total power radiated by the fluidic antenna to the powerdelivered to an input of the fluidic antenna.

Regarding an example of an apparatus for deforming (e.g., stretching) afluidic antenna to minimize human bias in measurements, a devicecontaining no metal parts may be used to avoid electronic coupling withthe antenna and may improve interpretation of results. Such a device mayconsist of two clamps formed of plastic (e.g., Delrin) that each grabone end of the fluidic antenna. The clamps may be formed to slide alongglass rods parallel to a length axis of the fluidic antenna. Plasticscrews may be used to exert a force that separates the two clamps,thereby causing the fluidic antenna to elongate in a controlled manner.It is understood that a person of ordinary skill would be capable offabricating such a device based upon the description above.

The liquid metal in the elastomer may maintain its electrical continuityduring stretching to provide circuit connectivity andtransmission/reception capabilities during stretching and contraction ofthe fluidic antenna. Although the cross-sectional area of the fluidicantenna reduces during elongation to maintain its total volume (e.g.,the Poisson ratio of PDMS is 0.5), the length of the liquid metal may bedirectly proportional to the length of elastomer within which it isenclosed.

FIG. 6 is an illustration of an example of an implementation of a set ofresonant frequency response curves 600 for a fluidic dipole antenna,such as the fluidic antenna 500, under different strain conditions(e.g., tension and compression forces). As described above, elongatingthe fluidic antenna may change (e.g., modulate) the spectral response.Additionally, where a fluidic antenna is mounted with a biasedelongation that results in a biased resonant frequency response, acompressive force that allows contraction of the fluidic antenna mayalso change (e.g., modulate) the spectral response. As such, the fluidicantennas may be used to sense strain (e.g., tension and compressionforces).

A resonance frequency (or biased resonant frequency) of a fluidicantenna may be determined within a lab or during a strain sensinginstallation using a radio frequency network analyzer, spectrumanalyzer, or similar circuitry, as appropriate for a givenimplementation. A reflection coefficient below negative ten decibels(−10 dB) may be considered sufficient for effective radiation incommercial antennas. The spectral response may be recorded as a functionof the length of the antenna (measured for example using calipers) atmillimeter (e.g., 2 mm) increments. The results may be plotted as aseries of curves.

As can be seen within FIG. 6, a biased resonant frequency curve 602represents, within the present example, an example biased elongation ofinstallation of a fluidic antenna. For a given elongation from the biasinstallation length, such as a measurable millimeter elongation (e.g., 4mm), an example first tension resonant frequency curve 604 represents alower resonant frequency. If the fluidic antenna is stretched further,such as another measurable millimeter elongation (e.g., another 4 mm),an example second tension resonant frequency curve 606 represents asecond lower resonant frequency. If the fluidic antenna is returned toits original biased installation elongation and a compressive force isapplied such that the fluidic antenna is allowed to contract (e.g., 4 mmrelative to the biased elongation) due to the elastomeric properties ofthe materials that enclose the liquid metal, an example contractionresonant frequency curve 608 represents a higher resonant frequency.

As such, resonant frequency of the fluidic antennas described herein maybe used to determine stress/strain on a structure. The resonantfrequency of the fluidic antenna may decrease with increasing antennalength. Further, it should be noted that resonant frequency during arelease of an applied strain may allow a fluidic antenna to return toits default elongation (e.g., biased for a biased installation) withoutexhibiting hysteresis. Accordingly, a fluidic antenna may be consideredreversibly stretchable and the resonant frequency indicative of thelength of a fluidic antenna regardless of whether strain is increasingor decreasing. However, it is understood that as described above,dimensions of a base material and substrate may be chosen as appropriatefor a given implementation to avoid fatigue or destruction of the basematerial and substrate during applied stresses or strains.

It is also understood that the axes relative to which the set ofresonant frequency response curves 600 are presented within FIG. 6 arefor purposes of example. Other axes or resolution of axes may beappropriate based upon the given implementation.

With further consideration for simulation and verification,computational electromagnetic methods and simulators, such as, forexample, a finite element model (FEM) method and simulator or othercomputational electromagnetic simulator may be used as appropriate for agiven implementation to model the resonant frequency of a fluidicantenna as a function of induced strain. An input file, such as acomputer-aided design (CAD) file input or other file as appropriate fora given implementation, used as input into the simulator may be used toidentify physical geometries and electric properties of each elementwithin and surrounding a fluidic antenna. Such a model may further beimplemented to account for geometry change of a fluidic antenna (as afunction of strain), the presence of an elastomer dielectric (e.g.,PDMS), and the surrounding clamping fixture to be utilized in the givenimplementation. Simulated resonance frequency may then be compared witha measured resonance frequency, both prior to and in the context ofapplied stress.

FIG. 7 is a block diagram of an example of an implementation of a strainsensing system 700 that utilizes the reversibly deformable andmechanically tunable dipole (dual element) fluidic antenna 500 (fluidicantenna 500 hereafter) of FIG. 5. The fluidic antenna 500 is shownmounted to a structural abutment presented by a structural member 702and a structural member 704. As can be seen from FIG. 7, the fluidicantenna 500 spans a gap between the structural member 702 and thestructural member 704. While the present example shows the fluidicantenna 500 mounted across a gap between the structural member 702 andthe structural member 704, this should not be considered limiting as thefluidic antenna 500 may be mounted to a solid section of a structuralmember and materials may be selected for construction of a fluidicantenna for sensing elongation and contraction of a single structuralmember in conjunction with a coefficient of linear expansion of therespective structural member without departure from the scope of thepresent subject matter. Additionally, the structural member 702 and thestructural member 704 may include one or more portions of a flexiblefabric or other material as described above.

A balun 706 couples a transmitter device 708 to the fluidic antenna 500as described in more detail above in FIG. 5. The transmitter device 708generates a signal that is propagated by the fluidic antenna 500. Thesignal may include any signal appropriate for a given implementation,such as for example, a continuous sinusoidal signal, or any other signalappropriate for a given implementation. The signal may further includeinformation, such as identifying information that identifies the fluidicantenna 500, within a given installation. For example, for animplementation that includes multiple fluidic antennas, radio frequencyidentification (RFID) may be used to identify a signal transmitted byeach of a group of transmitter devices, such as the transmitter device708. As such, RFID, or other technologies may be used to identifysignals generated by multiple fluidic antennas.

A receiver device 710 may receive the signal generated by thetransmitter device 708 via a receiving antenna 712. The receivingantenna 712 may be a rigid antenna, but may also be a fluidic antenna orother antenna as appropriate for a given implementation. Regarding useof a fluidic antenna as the receiving antenna 712, a fluidic receivingantenna may be mounted to an assembly that allows mechanical controlelements (not shown) of the receiver device 710 to stretch the fluidicreceiving antenna, and power of a received signal may be determinedwhere a maximum received power may be correlated with a current lengthof the fluidic receiving antenna to determine a resonant frequency ofthe fluidic antenna 500. As such, length matching may be utilized viapower measurement between transmitting and receiving fluidic antennas.Alternatively, a single rigid antenna may be used with spectral analysisto identify a resonant frequency of the fluidic antenna 500, or an arrayof rigid antennas may be used in a similar manner, each tuned to adifferent frequency. Many other possibilities exist for determination ofa resonant frequency of a fluidic antenna, such as the fluidic antenna500, and all are considered within the scope of the present subjectmatter.

As described above, the signal generated by the transmitter device 708may change frequency as the fluidic antenna 500 elongates or contractsbased upon tensile or compressive forces generated by the structuralmember 702 and the structural member 704, respectively. As such, thereceiver device 710 may detect a resonant frequency of the signalgenerated by the transmitter device 708 as modified by the strain/stressapplied on the structural member 702 and the structural member 704, asrepresented by a resonant frequency of the fluidic antenna 500. Thereceiver device 710 may process the received frequency to determine theresonant frequency of the fluidic antenna 500 and may determine atensile or compressive force applied by the structural member 702 andthe structural member 704.

As described above, the fluidic antenna 500 may be mounted with a biasedelongation that results in a biased resonant frequency of the fluidicantenna 500. As such, a tensile force may be determined by detection viathe receiver device 710 of a lower resonant frequency relative to thebiased resonant frequency of the fluidic antenna 500. Similarly, acompressive force may be determined by detection via the receiver device710 of a higher resonant frequency relative to the biased resonantfrequency of the fluidic antenna 500. For a non-biased installation,tensile strain may be sensed via a lower resonant frequency relative tothe fluidic antenna 500 and relative to a resting (e.g., non-elongated)resonant frequency.

Additionally, as described above, where multiple fluidic antennas areutilized within a given implementation, one or more receiver devices,such as the receiver device 710, may be used to determine an RFIDassociated with each installed fluidic antenna and may determine astrain/stress applied to each such fluidic antenna. Many otherpossibilities exist for wireless communications, wireless strainsensing, and fluidic antenna identification, and all are consideredwithin the scope of the present subject matter.

It should be noted that the transmitter device 708 and the receiverdevice 710 may be incorporated into the same physical device withoutdeparture from the scope of the present subject matter. As such,reference to either device may be considered a reference to the other asappropriate for a given implementation. It should also be understoodthat the transmitter device 708 and the receiver device 710 may eachinclude one or more processors, memories, communication modules, userinput modules, user output modules, and processing modules to performthe subject matter described herein for strain sensing.

A processing module 714 associated with the transmitter device 708 and aprocessing module 716 associated with the receiver device 710 mayperform the subject matter described herein for strain sensing. Theprocessing module 714 may transmit a signal, such as described above,that may alternatively include RFID or other information. The processingmodule 716 may receive and process such a signal.

The processing module 714 and the processing module 716 may beimplemented as a combination of hardware and software components, or asa collection of circuit components, as a custom integrated circuit(e.g., an application specific integrated circuit (ASIC)), as a fieldprogrammable gate array (FPGA) programmed processing module, or othercircuitry. The processing module may form a portion of other circuitrydescribed without departure from the scope of the present subjectmatter.

Further, such a processing module may alternatively be implemented as anapplication stored within a memory and executed by one or moreprocessor. In such an implementation, a processing module may includeinstructions executed by one or more processors for performing thefunctionality described herein. The processor(s) may execute theseinstructions to provide the processing capabilities described above andin more detail below for a device, such as the receiver device 710. Theprocessing module may form a portion of an interrupt service routine(ISR), a portion of an operating system, a portion of a browserapplication, or a portion of a separate application without departurefrom the scope of the present subject matter.

It should be noted that the receiver device 710 may be stationary andattached proximate to a structure or may be a portable computing device,either by a user's ability to move the receiver device 710 to differentlocations, or by the receiver device 710's association with a portableplatform, such as a plane, train, automobile, or other moving vehicle.For example, where the receiver device 710 is associated with a movingvehicle (e.g., a train) that regularly travels a path that includes abridge, the receiver device 710 may log (e.g., store) straindeterminations over time and make additional strain determinationsduring each traverse of the respective bridge. Comparisons, such asstatistical deviations or other mathematical processing, of currentstrain determinations with historic strain determinations may beperformed to determine deviations from expected strain results. Suchdeviations may be used to predict reliability or failure of a givenstructural element, such as a bridge.

Similarly, the receiver device 710 may be collocated with a structure,such as a bridge, and receive RFID information and other informationfrom passing vehicles, such as weight of each vehicle, to determinedifferences in strain for different loads. These determined differencesin strain may be used to predict reliability or failure of a givenstructural element, such as a bridge.

It should also be noted that the receiver device 710 may be anycomputing device capable of processing information as described aboveand in more detail below. For example, the receiver device 710 mayinclude devices such as a personal computer (e.g., desktop, laptop, ahandheld device (e.g., cellular telephone, personal digital assistant(PDA), email device, etc.), or any other device capable of processinginformation as described in more detail below.

The receiver device may further be interconnected via a network (notshown) for communication of strain sensing determinations to otherlocations for storage or additional processing. The network may includeany form of interconnection suitable for the intended purpose, includinga private or public network such as an intranet or the Internet,respectively, direct inter-module interconnection, dial-up, wireless, orany other interconnection mechanism capable of interconnecting therespective devices.

As such, the receiver device 710 may include an entirely embedded devicethat communicates strain determinations without mechanically coupleduser interface input or output capabilities. A wireless user interfacemay also be provided for the receiver device 710, as appropriate for agiven implementation. For example, a passing vehicle on a bridge mayquery an RFID of each receiver device, such as the receiver device 710,and log (e.g., store) strain determinations. Many possibleimplementations exist for a receiver device, such as the receiver device710, and all are considered within the scope of the present subjectmatter.

FIG. 8 through FIG. 11 below describe example processes that may beexecuted by devices, such as a manufacturing device or devices such asthe receiver device 710, for processing associated with reversiblydeformable and mechanically tunable fluidic antennas. Many othervariations on the example processes are possible and all are consideredwithin the scope of the present subject matter. It should be noted thattime out procedures and other error control procedures are notillustrated within the example processes described below for ease ofillustration purposes. However, it is understood that all suchprocedures are considered to be within the scope of the present subjectmatter.

FIG. 8 is a flow chart of an example of an implementation of a process800 for manufacturing a reversibly deformable and mechanically tunablefluidic antenna as a fluidic structure. At block 802, the process 800forms a cavity that defines a shape of an element of the fluidicstructure within a material. At block 804, the process 800 fills thecavity with liquid metal. At block 806, the process 800 seals thecavity, where the fluidic structure behaves as an antenna.

FIG. 9 is a flow chart of an example of an implementation of a process900 for manufacturing a reversibly deformable and mechanically tunablefluidic antenna using a two-part substrate. At decision point 902, theprocess 900 makes a determination as to whether to form a fluidicantenna. In response to determining to form a fluidic antenna, theprocess 900 forms a base material with at least one antenna channel thatdefines a shape of an element of the fluidic antenna within a basematerial. As described above, a base material may include an elastomericbase material made via a negative photoresist process, lithography,injection molding, imprinting, molding, stamping, and milling thematerial, or other process as appropriate for a given implementation. Atblock 906, the process 900 seals a flat substrate to the base materialto form a completed substrate for the fluidic antenna. Sealing the flatsubstrate to the base material may include coupling an elastomer bondinglayer material to an elastomer base material portion that seals a lengthof the at least one channel. It should be understood that while thepresent example utilizes a flat substrate, many other substrateformations are possible. For example, a substrate may also include acavity or form another shape for sealing a length of the at least onechannel. Accordingly, any such substrate is considered within the scopeof the present subject matter.

At block 908, the process 900 injects or draws liquid metal into eachchannel in the substrate and terminates filling when the metal is in thedesired shape. At block 910, the process 910 seals inlet and outletfilling holes to complete formation of the fluidic antenna.

It should be noted that the process 900 may be performed in situ or exsitu. For in situ operations, the base material may be coupled to acircuit assembly and the channel filled with the liquid metal in situwhile the material is coupled to the circuit assembly. Further, becausethe liquid metal is liquid at room temperature, the channel may befilled with the liquid metal at room temperature.

FIG. 10 is a flow chart of an example of an implementation of a process1000 for determining a strain on one or more structural elements using areversibly deformable and mechanically tunable fluidic antenna. Atdecision point 1002, the process 1000 receives, via a receiving antennaof a computing device, a radio frequency signal transmitted via afluidic antenna coupled to a structural element, where at least oneliquid metal antenna element is formed within a material that defines anelastomeric mechanical property of the fluidic antenna and spectraltransmission characteristics of the fluidic antenna change in responseto changes in shape of the fluidic antenna. At block 1004, the process1000 determines a resonant frequency of the radio frequency signal. Atblock 1006, the process 1000 determines a strain on the structuralelement based upon the determined resonant frequency of the radiofrequency signal.

FIG. 11 is a flow chart of an example of an implementation of a process1100 for determining a strain on one or more structural elements using aset of reversibly deformable and mechanically tunable fluidic antennasand logging device identifiers associated with determined strainreading. At decision point 1102, the process 1100 makes a determinationas to whether a radio frequency signal has been received from a devicetransmitting via a fluidic antenna, such as the transmitter device 708and the fluidic antenna 500. It should be noted that the process 1100may iteratively process one or more fluidic antenna resonant frequencyreceptions associated with one or more fluidic antennas or changes inresonant frequency of a currently received fluidic antenna resonantfrequency. It is further noted that the process 1100 may be implementedto concurrently process more than one fluidic antenna resonant frequencyinput as appropriate for a given implementation.

In response to determining that a radio frequency signal has beenreceived at decision point 1102, the process 1100 processes the receivedsignal via spectral analysis at block 1104. At block 1106, the process1100 determines a resonant frequency of the radio frequency signal basedupon the spectral analysis.

At decision point 1108, the process 1100 makes a determination as towhether a radio frequency identifier (RFID) is associated with thereceived radio frequency signal and fluidic antenna. In response todetermining that an RFID is associated with the received radio frequencysignal and fluidic antenna, the process 1100 logs the fluidic antennaRFID at block 1110. In response to completion of logging the fluidicantenna RFID or determining that no RFID is associated with the antennaat decision point 1108, the process 1100 makes a determination as towhether the fluidic antenna is mounted in a biased (e.g., elongated)installation at decision point 1112. As described above, a fluidicantenna may be mounted in a biased installation to allow detection ofboth expansion and contraction (e.g., tensile strain and compressivestrain, respectively) of structural elements, such as structuralelements of a building, bridge, fabric (e.g., a bandage), or otherstructural elements.

In response to determining that the fluidic antenna is not mounted in abiased installation, the process 1100 compares the determined resonantfrequency with an unstressed resonant frequency of the fluidic antennaat block 1114. At block 1116, the process 1100 determines a deviation ofthe determined resonant frequency relative to the unstressed resonantfrequency of the fluidic antenna. It is understood that for non-biasedinstallations, a determined deviation in resonant frequency may includea change to a lower frequency as a result of elongation (e.g.,stretching) of the fluidic antenna in response to tensile strain.

Returning to the description of decision point 1112, in response todetermining that the fluidic antenna is mounted in a biasedinstallation, the process 1100 compares the determined resonantfrequency with the biased resonant frequency of the fluidic antenna atblock 1118. At block 1120, the process 1100 determines a deviation ofthe determined resonant frequency relative to the biased resonantfrequency of the fluidic antenna. It is understood that for biasedinstallations, a determined deviation in resonant frequency may includea change to a higher frequency or a lower frequency as a result of adecrease in biased length or elongation (e.g., stretching) of thefluidic antenna in response to compressive strain or tensile strain,respectively.

At decision point 1122, the process 1100 makes a determination as towhether the deviation of the determined resonant frequency relative tothe biased resonant frequency is a higher frequency or a lower frequencyrelative to the biased resonant frequency. In response to determiningthat the deviation of the determined resonant frequency relative to thebiased resonant frequency is a higher frequency, the process 1100determines the compressive strain on the structure in response todetermining that the determined frequency comprises the higher frequencyat block 1124. In response to determining that the deviation of thedetermined resonant frequency relative to the biased resonant frequencyis a lower frequency at decision point 1122, or in response tocompletion of determining the deviation for the non-biased installationof a fluidic antenna at block 1116, the process 1100 determines thetensile strain on the structure in response to determining that thedetermined frequency comprises the lower frequency at block 1126. Asdescribed above with respect to block 1116, for non-biasedinstallations, a determined deviation in resonant frequency may includea change to a lower frequency as a result of elongation (e.g.,stretching) of the fluidic antenna in response to tensile strain.

At block 1128, the process 1100 logs the determined strain on thestructural element along with the fluidic antenna RFID, if received. Theprocess 1100 then returns to decision point 1102 to await receipt of anew signal or a change in resonant frequency of a currently receivedfluidic antenna resonant frequency.

As such, the process 1100 may receive and process resonant frequencyinformation for one or more fluidic antennas. The process 1100 maydetermine compressive strain on a structure when a fluidic antenna ismounted in a biased installation, and may determine tensile strain foreither biased or non-biased installations. The process 1100 may processone or multiple fluidic antennas to determine strain for one or multiplestrain sensing locations, as appropriate for a given implementation,where RFID or other similar technology is employed to identify which ofmultiple strain sensing locations is being processed. Many othervariations on the processing described are possible and all areconsidered within the scope of the present subject matter.

Based upon the subject matter described herein, fluidic antennas may bedeformed reversibly (e.g., stretched, bent, rolled, wrapped, folded,etc.) without loss of electrical continuity. Furthermore, in response tosuch deformations, fluidic antennas may exhibit an equivalent spectralresponse before and after deformation. As such, fluidic antennas basedupon the present subject matter may be considered reversibly deformable.Further, durability may be improved over conventional solid metalantennas due to a lack of hysteresis in response to deformation.

Relative to conventional copper antennas, the fluidic antennas asdescribed herein provide several advantages. For example, the fluidicantennas may be considered reversibly deformable and durable. Theelastomeric casing may define the mechanical properties of the fluidicantenna and the fluid metal flows in response to deformation to maintainelectrical continuity. Additionally, the fluidic antennas may beconsidered mechanically tunable and sensitive to strain. Further, theliquid metal may form contacts with baluns at room temperature withoutsoldering. As another example, the low modulus and low surface energy ofelastomers such as PDMS allows the fluidic antennas to conform tonumerous surfaces. Also, the fluidic antenna may self-heal in responseto sharp cuts that leave sufficient elastomer intact to allow theelastomer to reform to its original shape. Additionally, the fabricationof the antenna by soft-lithography may allow many antennas to beproduced from a single lithographic master. These advantages list a fewof the advantages of the technology described herein.

As described above in association with FIG. 1 through FIG. 11, theexample systems and processes provide manufacturing of reversiblydeformable and mechanically tunable fluidic antennas, and examples ofsensing and communicating information using such antennas. Many othervariations and additional activities associated with reversiblydeformable and mechanically tunable fluidic antennas are possible andall are considered within the scope of the present subject matter.

Those skilled in the art will recognize, upon consideration of the aboveteachings, that certain of the above examples are based upon use of aprogrammed processor. However, the invention is not limited to suchexample embodiments, since other embodiments could be implemented usinghardware component equivalents such as special purpose hardware and/ordedicated processors. Similarly, general purpose computers,microprocessor based computers, micro-controllers, optical computers,analog computers, dedicated processors, application specific circuitsand/or dedicated hard wired logic may be used to construct alternativeequivalent embodiments.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A method, comprising: receiving, via a receivingantenna of a computing device, a radio frequency signal transmitted viaa fluidic antenna coupled to a structural element, where at least oneliquid metal antenna element is formed within a material that defines anelastomeric mechanical property of the fluidic antenna and wherespectral transmission characteristics of the fluidic antenna change inresponse to changes in shape of the fluidic antenna; determining aresonant frequency of the radio frequency signal; and determining astrain on the structural element based upon the determined resonantfrequency of the radio frequency signal.
 2. The method of claim 1, wheredetermining the resonant frequency of the radio frequency signalcomprises: processing the radio frequency signal via spectral analysis;and determining the resonant frequency of the radio frequency signalbased upon output of the spectral analysis.
 3. The method of claim 1,where determining the strain on the structural element based upon thedetermined resonant frequency of the radio frequency signal comprises:comparing the determined resonant frequency with an unstrained resonantfrequency of the fluidic antenna; determining a deviation of thedetermined resonant frequency relative to the unstrained resonantfrequency of the fluidic antenna; and determining the strain on thestructural element based upon the determined deviation of the determinedresonant frequency relative to the unstrained resonant frequency of thefluidic antenna.
 4. The method of claim 1, where the fluidic antenna iscoupled to the structural element with a biased elastomeric strainresulting in a biased resonant frequency, and where determining thestrain on the structural element based upon the determined resonantfrequency comprises determining one of a compressive strain and atensile strain on the structural element based upon the determinedresonant frequency.
 5. The method of claim 4, where determining the oneof the compressive strain and the tensile strain on the structuralelement based upon the determined resonant frequency comprises:comparing the determined resonant frequency with the biased resonantfrequency of the fluidic antenna; determining a deviation of thedetermined resonant frequency relative to the biased resonant frequencyof the fluidic antenna; determining whether the deviation of thedetermined resonant frequency relative to the biased resonant frequencycomprises one of a higher frequency and a lower frequency relative tothe biased resonant frequency; determining the compressive strain on thestructural element in response to determining that the determinedresonant frequency comprises the higher frequency; and determining thetensile strain on the structural element in response to determining thatthe determined resonant frequency comprises the lower frequency.
 6. Themethod of claim 1, further comprising: determining a radio frequencyidentifier (RFID) associated with a device that transmitted the radiofrequency signal; logging the RFID associated with the device thattransmitted the radio frequency signal; and logging the determinedstrain on the structural element.